The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
Powertrains in motor vehicles require lubrication and cooling using a hydraulic fluid to continuously operate. More specifically, the engine and especially the automatic transmission require lubricating and hydraulic fluids or oils to maintain their operation and extend their useful life. The hydraulic fluid is communicated throughout the transmission via hydraulic passages and controls. For example, a typical rear wheel drive planetary transmission architecture contains two ‘sections’: a barrel section containing the gear train assembly and a sump section located below the gear train containing hydraulic controls. Transmissions use oil pans to collect and store oil as a source of oil for an oil pump that distributes it under pressure throughout the transmission. The pans may be wet sump or dry sump, the former storing a larger volume of oil than the latter.
The barrel section of the transmission typically has a large clearance between the rotating components and the transmission case or housing. This large clearance is due in part to the nature of aluminum casting draft and various transmission architectures chosen that define the shape of the transmission case. A large clearance between the rotating components and the transmission case is particularly unwanted as vehicle performance envelopes increase; maneuver volumes force hydraulic fluid into rotating components through fluid transfers designed to drain the oil from the gear train. Accordingly, excess hydraulic fluid collects on the rotating components. As the components rotate, centrifugal force throws this oil from the parts. The thrown hydraulic fluid, being uncontrolled, causes splash from contact with the oil pan (or controls) and with hydraulic fluid already in the collection volume of the oil pan. The hydraulic fluid splashing back onto the rotating assembly induces hydraulic drag from the fluid impact. In addition, the wind created by the rotating gear train creates additional splash by contacting the oil in the collection volume of the oil pan.
The loss associated with wind related splash is known as windage loss while that of thrown oil is referred to as oil impact loss. The consequence of too much hydraulic fluid on rotating is more than mere friction. Hydraulic fluid on the rotating parts has a mass which must be accelerated during engine acceleration which acts as a loss on efficiency.
In addition, the splashing hydraulic fluid leads to aeration of the hydraulic fluid. High proportions of dissolved air in the hydraulic fluid can in turn lead to pump cavitation and excessive softness in hydraulic-actuator force-versus-displacement characteristics. The dissolved air can also reduce the effectiveness of hydraulic fluid lubrication and cooling properties. Accordingly, there is a need in the art for a device for reducing the clearance between the rotating components in the transmission and the transmission case wall in order to reduce hydraulic fluid splash in order to reduce drag losses and aeration.